Many species experience social stressors during their lifetimes. This is especially true for humans, whose overwhelming source of conflict and stress is social in nature. A large body of evidence suggests that exposure to traumatic events or persistent high levels of stress are linked to the development and expression of a number of stress-related disorders (i.e. PTSD, depression, anxiety disorders). Animal models of stress-related disorders have provided important information about the neurobiological basis of many psychopathologies. Very few models, however, have examined these disorders in a biologically relevant paradigm. Conditioned defeat in Syrian hamsters provides an ideal model for studying the neurobiological basis of stress-related disorders in an ecologically relevant context. The goal of the current proposal is to explore the neuroanatomical and neurochemical basis of conditioned defeat by using site-specific microinjections into specific brain nuclei. The present proposal will test the hypothesis that the brain areas and neurochemicals that are involved in fear, anxiety and behavioral responses to stressors, in general, are also critical in the acquisition and expression of conditioned defeat. The results of the current proposal will provide important insight into the underlying physiological mechanisms of conditioned defeat. Additionally, these data will contribute to our knowledge about the neurobiological basis of human stress-related disorders.